Such cable transmissions have been known (see, e.g., DE-PS 2 021 580). The extension arms, of which there are, in general, two and which form the solar generators of the spacecraft, are thus unfolded. To unfold the extension arms, the movement processes of the individual solar panels must be synchronized with the cable transmissions in order for, e.g., the center of gravity of each extension arm to move during unfolding along a predetermined path and for the individual parts of the extension arm to reach the unfolded position with controlled movements.
However, the exact synchronization of the movement processes of the solar panels during the unfolding of the extension arms is associated with difficulties. Thus, strong tensile forces occur during unfolding on the cable, which lead to elongation of the cable. In addition, compared with the temperature at which the transmission is mounted, the cables are exposed to temperatures of about .+-.100.degree. K under the operating conditions in the space. Since the cable has a greater coefficient of thermal expansion than the panels, which are designed as, e.g., carbon fiber-reinforced plastic sandwiches, slackening of the cable occurs at high temperatures. To prevent this from happening, the pretension of the cable must be additionally increased. Thus, very strong tensile forces act at low temperatures on the cable pulleys, which may lead to a high load on the hinges and on the solar panels, and they may considerably increase the friction in the hinges.
To ensure a defined pretension of the cables despite the greatly varying operating temperatures, it has been known that tension springs may be installed in the cables. However, a new problem is thus created.
The drive for the unfolding process is formed by, e.g., driving springs between the panels, which act on the cable pulley, on the one hand, and, on the other hand, on the panel, at which the cable pulley is mounted rotatably. To prevent the panels from shooting out to the outside uncontrollably due to these driving springs during the unfolding process, but to ensure that they are folded out at a predetermined velocity, the rotary movement of the innermost hinge, i.e., of the hinge by which the so-called yoke is connected to the spacecraft, is decelerated or, if necessary, driven, in general, with, e.g., a self-locking transmission. This preset speed of rotation of the innermost hinge shall then be transmitted by the cable transmissions to the other hinges.
However, this is not possible if the cables are provided with tension springs, because the tension springs will then lead to an uncontrolled elastic withdrawal and extension of the individual panels during unfolding.
Since the panels of each extension arm are located in one plane in the unfolded end position, corresponding locking means, which snap in automatically when the end position is reached, are, in general, provided. Thus, even a premature snapping in of the locking means may occur between two panels due to the uncontrolled extension based on the tension springs in the cables of the cable transmission, which leads to a completely uncontrolled unfolding process.
A cable consisting of threads provided with a binder envelope, e.g., glass threads, which are wound helically, has been known from DE 28 18 549 A1. The binder is used in such an amount that the length of the cable can be controlled under varying temperature conditions by causing a change in the cross-sectional area of the cable opposite the change in the length of the threads.